java.io

Interface DataInput

All Known Implementing Classes:

DataInputStream

public interface DataInput

This interface is implemented by classes that can data from streams into Java primitive types.

Author:

Aaron M. Renn (arenn@urbanophile.com), Warren Levy (warrenl@cygnus.com)

Method Summary

Modifier and Type	Method and Description
boolean	readBoolean() This method reads a Java boolean value from an input stream.
byte	readByte() This method reads a Java byte value from an input stream.
char	readChar() This method reads a Java char value from an input stream.
double	readDouble() This method reads a Java double value from an input stream.
float	readFloat() This method reads a Java float value from an input stream.
void	readFully(byte[] buf) This method reads raw bytes into the passed array until the array is full.
void	readFully(byte[] buf, int offset, int len) This method reads raw bytes into the passed array buf starting offset bytes into the buffer.
int	readInt() This method reads a Java int value from an input stream It operates by reading four bytes from the stream and converting them to a single Java int.
String	readLine() This method reads the next line of text data from an input stream.
long	readLong() This method reads a Java long value from an input stream It operates by reading eight bytes from the stream and converting them to a single Java long.
short	readShort() This method reads a signed 16-bit value into a Java in from the stream.
int	readUnsignedByte() This method reads 8 unsigned bits into a Java int value from the stream.
int	readUnsignedShort() This method reads 16 unsigned bits into a Java int value from the stream.
String	readUTF() This method reads a String from an input stream that is encoded in a modified UTF-8 format.
int	skipBytes(int numBytes) This method skips and discards the specified number of bytes in an input stream.

Method Detail

readBoolean

boolean readBoolean()
             throws EOFException,
                    IOException

This method reads a Java boolean value from an input stream. It does so by reading a single byte of data. If that byte is zero, then the value returned is false. If the byte is non-zero, then the value returned is true.

This method can read a boolean written by an object implementing the writeBoolean() method in the DataOutput interface.

Returns:

The boolean value read

Throws:

EOFException - If end of file is reached before reading the boolean

IOException - If any other error occurs

See Also:

DataOutput.writeBoolean(boolean)

readByte

byte readByte()
       throws EOFException,
              IOException

This method reads a Java byte value from an input stream. The value is in the range of -128 to 127.

This method can read a byte written by an object implementing the writeByte() method in the DataOutput interface.

Returns:

The byte value read

Throws:

EOFException - If end of file is reached before reading the byte

IOException - If any other error occurs

See Also:

DataOutput.writeByte(int)

readChar

char readChar()
       throws EOFException,
              IOException

This method reads a Java char value from an input stream. It operates by reading two bytes from the stream and converting them to a single 16-bit Java char. The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 and byte2 represent the first and second byte read from the stream respectively, they will be transformed to a char in the following manner:

(char)((byte1 << 8) + byte2)

This method can read a char written by an object implementing the writeChar() method in the DataOutput interface.

Returns:

The char value read

Throws:

EOFException - If end of file is reached before reading the char

IOException - If any other error occurs

See Also:

DataOutput.writeChar(int)

readDouble

double readDouble()
           throws EOFException,
                  IOException

This method reads a Java double value from an input stream. It operates by first reading a long value from the stream by calling the readLong() method in this interface, then converts that long to a double using the longBitsToDouble method in the class java.lang.Double.

This method can read a double written by an object implementing the writeDouble() method in the DataOutput interface.

Returns:

The double value read

Throws:

EOFException - If end of file is reached before reading the double

IOException - If any other error occurs

See Also:

DataOutput.writeDouble(double), Double.longBitsToDouble(long)

readFloat

float readFloat()
         throws EOFException,
                IOException

This method reads a Java float value from an input stream. It operates by first reading an int value from the stream by calling the readInt() method in this interface, then converts that int to a float using the intBitsToFloat method in the class java.lang.Float.

This method can read a float written by an object implementing the writeFloat() method in the DataOutput interface.

Returns:

The float value read

Throws:

EOFException - If end of file is reached before reading the float

IOException - If any other error occurs

See Also:

DataOutput.writeFloat(float), Float.intBitsToFloat(int)

readFully

void readFully(byte[] buf)
        throws EOFException,
               IOException

This method reads raw bytes into the passed array until the array is full. Note that this method blocks until the data is available and throws an exception if there is not enough data left in the stream to fill the buffer. Note also that zero length buffers are permitted. In this case, the method will return immediately without reading any bytes from the stream.

Parameters:

buf - The buffer into which to read the data

Throws:

EOFException - If end of file is reached before filling the buffer

IOException - If any other error occurs

readFully

void readFully(byte[] buf,
               int offset,
               int len)
        throws EOFException,
               IOException

This method reads raw bytes into the passed array buf starting offset bytes into the buffer. The number of bytes read will be exactly len. Note that this method blocks until the data is available and throws an exception if there is not enough data left in the stream to read len bytes. Note also that zero length buffers are permitted. In this case, the method will return immediately without reading any bytes from the stream.

Parameters:

buf - The buffer into which to read the data

offset - The offset into the buffer to start storing data

len - The number of bytes to read into the buffer

Throws:

EOFException - If end of file is reached before filling the buffer

IOException - If any other error occurs

readInt

int readInt()
     throws EOFException,
            IOException

This method reads a Java int value from an input stream It operates by reading four bytes from the stream and converting them to a single Java int. The bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 through byte4 represent the first four bytes read from the stream, they will be transformed to an int in the following manner:

(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) + ((byte3 & 0xFF)<< 8) + (byte4 & 0xFF)))

The value returned is in the range of -2147483648 to 2147483647.

This method can read an int written by an object implementing the writeInt() method in the DataOutput interface.

Returns:

The int value read

Throws:

EOFException - If end of file is reached before reading the int

IOException - If any other error occurs

See Also:

DataOutput.writeInt(int)

readLine

String readLine()
         throws IOException

This method reads the next line of text data from an input stream. It operates by reading bytes and converting those bytes to char values by treating the byte read as the low eight bits of the char and using 0 as the high eight bits. Because of this, it does not support the full 16-bit Unicode character set.

The reading of bytes ends when either the end of file or a line terminator is encountered. The bytes read are then returned as a String. A line terminator is a byte sequence consisting of either \r, \n or \r\n. These termination charaters are discarded and are not returned as part of the string. A line is also terminated by an end of file condition.

Returns:

The line read as a String

Throws:

IOException - If an error occurs

readLong

long readLong()
       throws EOFException,
              IOException

This method reads a Java long value from an input stream It operates by reading eight bytes from the stream and converting them to a single Java long. The bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 through byte8 represent the first eight bytes read from the stream, they will be transformed to an long in the following manner:

(long)(((byte1 & 0xFF) << 56) + ((byte2 & 0xFF) << 48) + ((byte3 & 0xFF) << 40) + ((byte4 & 0xFF) << 32) + ((byte5 & 0xFF) << 24) + ((byte6 & 0xFF) << 16) + ((byte7 & 0xFF) << 8) + (byte8 & 0xFF)))

The value returned is in the range of -9223372036854775808 to 9223372036854775807.

This method can read an long written by an object implementing the writeLong() method in the DataOutput interface.

Returns:

The long value read

Throws:

EOFException - If end of file is reached before reading the long

IOException - If any other error occurs

See Also:

DataOutput.writeLong(long)

readShort

short readShort()
         throws EOFException,
                IOException

This method reads a signed 16-bit value into a Java in from the stream. It operates by reading two bytes from the stream and converting them to a single 16-bit Java short. The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 and byte2 represent the first and second byte read from the stream respectively, they will be transformed to a short in the following manner:

(short)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))

The value returned is in the range of -32768 to 32767.

This method can read a short written by an object implementing the writeShort() method in the DataOutput interface.

Returns:

The short value read

Throws:

EOFException - If end of file is reached before reading the value

IOException - If any other error occurs

See Also:

DataOutput.writeShort(int)

readUnsignedByte

int readUnsignedByte()
              throws EOFException,
                     IOException

This method reads 8 unsigned bits into a Java int value from the stream. The value returned is in the range of 0 to 255.

This method can read an unsigned byte written by an object implementing the writeByte() method in the DataOutput interface.

Returns:

The unsigned bytes value read as a Java int.

Throws:

EOFException - If end of file is reached before reading the value

IOException - If any other error occurs

See Also:

DataOutput.writeByte(int)

readUnsignedShort

int readUnsignedShort()
               throws EOFException,
                      IOException

This method reads 16 unsigned bits into a Java int value from the stream. It operates by reading two bytes from the stream and converting them to a single Java int. The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 and byte2 represent the first and second byte read from the stream respectively, they will be transformed to an int in the following manner:

(int)(((byte1 0xFF) << 8) + (byte2 & 0xFF))

The value returned is in the range of 0 to 65535.

This method can read an unsigned short written by an object implementing the writeShort() method in the DataOutput interface.

Returns:

The unsigned short value read as a Java int.

Throws:

EOFException - If end of file is reached before reading the value

IOException - If any other error occurs

See Also:

DataOutput.writeShort(int)

readUTF

String readUTF()
        throws EOFException,
               UTFDataFormatException,
               IOException

This method reads a String from an input stream that is encoded in a modified UTF-8 format. This format has a leading two byte sequence that contains the remaining number of bytes to read. This two byte sequence is read using the readUnsignedShort() method of this interface. After the number of remaining bytes have been determined, these bytes are read an transformed into char values. These char values are encoded in the stream using either a one, two, or three byte format. The particular format in use can be determined by examining the first byte read.

If the first byte has a high order bit of 0, then that character consists on only one byte. This character value consists of seven bits that are at positions 0 through 6 of the byte. As an example, if byte1 is the byte read from the stream, it would be converted to a char like so:

(char)byte1

If the first byte has 110 as its high order bits, then the character consists of two bytes. The bits that make up the character value are in positions 0 through 4 of the first byte and bit positions 0 through 5 of the second byte. (The second byte should have 10 as its high order bits). These values are in most significant byte first (i.e., "big endian") order.

As an example, if byte1 and byte2 are the first two bytes read respectively, and the high order bits of them match the patterns which indicate a two byte character encoding, then they would be converted to a Java char like so:

(char)(((byte1 & 0x1F) << 6) + (byte2 & 0x3F))

If the first byte has a 1110 as its high order bits, then the character consists of three bytes. The bits that make up the character value are in positions 0 through 3 of the first byte and bit positions 0 through 5 of the other two bytes. (The second and third bytes should have 10 as their high order bits). These values are in most significant byte first (i.e., "big endian") order.

As an example, if byte1, byte2, and byte3 are the three bytes read, and the high order bits of them match the patterns which indicate a three byte character encoding, then they would be converted to a Java char like so: (char)(((byte1 & 0x0F) << 12) + ((byte2 & 0x3F) + (byte3 & 0x3F)) Note that all characters are encoded in the method that requires the fewest number of bytes with the exception of the character with the value of \<llll>u0000 which is encoded as two bytes. This is a modification of the UTF standard used to prevent C language style NUL values from appearing in the byte stream.

This method can read data that was written by an object implementing the writeUTF() method in DataOutput.

Returns:

The String read

Throws:

EOFException - If end of file is reached before reading the String

UTFDataFormatException - If the data is not in UTF-8 format

IOException - If any other error occurs

See Also:

DataOutput.writeUTF(java.lang.String)

skipBytes

int skipBytes(int numBytes)
       throws EOFException,
              IOException

This method skips and discards the specified number of bytes in an input stream. Note that this method may skip less than the requested number of bytes. The actual number of bytes skipped is returned. No bytes are skipped if a negative number is passed to this method.

Parameters:

numBytes - The number of bytes to skip

Returns:

The number of bytes actually skipped, which will always be numBytes

Throws:

EOFException - If end of file is reached before all bytes can be skipped

IOException - If any other error occurs